shale development and hydraulic fracturing or - center · pdf file ·...

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Shale Development and Hydraulic Fracturing

or

Frac’ing (Fracking) – What is it?

Dr. Will Fleckenstein, PE

Colorado School of Mines

P E T R O L E U M E N G I N E E R I N G D E P A R T M E N T

Who is involved in discussions on “Fracking”?

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Dr. Frackenstein

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2009

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The shale plays are widespread

Occur anywhere

conventional production

exists

How do you drill and complete these shales?

2011

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1000% Increase in horizontal rigs

Haynesville Results

Production is dropping

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Source: EIA, October 2013

Natural Gas Cheap Compared to Oil,

Driven by Shale Gas Production

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Crude oil

prices

Natural Gas

equivalent

prices

The shale plays are widely

separated, with different

geologic properties, but they

have one uniform effect:

They are driving down

natural gas prices in the US

Marcellus Well Results

Results continue to improve

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Source: EIA, October 2013

Marcellus Well Results

Wells are getting better

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What about Unconventional Oil Production?

- Bakken Production in North Dakota

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Is this Affecting US Oil Production?

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Drilling and Stimulating a Horizontal Shale Well

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1-4000 m

deep

300-3000 m

long

Fracture

stimulation

Horizontal

Well Vertical

Well

Vertical vs. Horizontal Drilling

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Each horizontal replaces

Many vertical wells

Important Horizontal Development Topics

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1. Drilling • Modern horizontal drilling began in 1990, with the widespread acceptance of MWD

(Measurement While Drilling) to steer the wellbore horizontally.

• This allowed the experimentation in the Barnett Shale by George Mitchell, resulting in

horizontal laterals, coupled with multi-stage fracturing, to develop shales

• Pad drilling

2. Casing • The curvature of wellbore meant that the casing had to curve also, resulting in connections

designed to withstand the torque and drag of a horizontal well

• The casing many times has to be rotated to bottom, driving the acceptance of top drives on

rigs, and special tools to facilitate this rotation

3. Cementing and Isolation • Special tools and cements were developed to isolate and cement these wellbores,

including expandable liner hangers, inflatable and “swellable” packers.

.

How do we drill a horizontal well?

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Change direction by rotating bit with

a downhole motor, or a rotary

steerable system – deflect the bit

Controlled curvature

Controlled direction

Geo-steering

Mud motor

Bit

“PDC” Bits

How do we drill a horizontal well?

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Drill straight by rotating the

drill string, so that the bit

is never pointed in a

single direction

Maintain direction of the

bit

Rotary steerable or mud

motor system

Drill string rotation may

or may not be necessary

Mud motor

Bit

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Why Stimulate?

Courtesy Ken Mahrer, Apex

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What Should be Done Prior to Horizontal Drilling?

1. Establish a baseline of potential contaminants

in aquifers

– Natural gas

– Natural dissolved solids

– Identification of pre-existing pollution

2. Identify barriers to hydraulic frac growth in the

reservoir

3. Construct a reservoir model, including

mechanical properties of rocks, identification

of natural fractures, amount and type of

hydrocarbons

4. Water sources and disposal

5. Logistics

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Colorado wellsite

Well Construction and Surface Disruption

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Drilling rigs are very large and result in 150 direct and indirect jobs per rig.

The drilling rig needs good roads, bridges etc. to move. The best rig move is

to not move very far, but to drill multiple wells from 1 pad (pad drilling).

Proper well siting allows

multiple wells to be drilled

from the same location.

The drilling rig “walks”

from well to the next,

minimizing time, costs and

allowing the least surface

disruption

Horizontal Drilling Project by Dr. Fleckenstein

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Six complicated wells drilled from a single

surface location in California amid other wells

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Typical Well Construction

Primary Cementing Objectives

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– Anchor the casing

– Protection casing against

corrosion and erosion

– Support borehole walls

– Zonal Isolation

Surface Casing

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1. The hole is drilled for the first string of casing.

2. The casing is then cemented in the wellbore

to the surface. Surface Casing Purpose

1. Protect Surface water

2. Anchor BOPE

3. Support casing strings

4. Well Control

Cementing Process

Colorado Example

Regulations Governing Surface Casing

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e. Surface casing where subsurface conditions are unknown. In areas

where pressure and formations are unknown, sufficient surface casing

shall be run to reach a depth below all known or reasonably estimated

utilizable domestic fresh water levels and to prevent blowouts or

uncontrolled flows and shall be of sufficient size to permit the use of an

intermediate string or strings of casings.

Surface casing shall be set in or through an impervious formation and

shall be cemented by pump and plug or displacement or other approved

method with sufficient cement to fill the annulus to the top of the hole, all in

accordance with reasonable requirements of the Director

Cementing Difficulties

© 2008

A.W.

Eustes 25

Hole may be washed out

Pipe may be not centered

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What can we see?

Casing head

Production Casing

Casing hanger

Tubing hanger

Tubing

Surface Casing Cement

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3 Key Elements of Horizontal Multistage Fracturing

1. Water fracs

2. Microseismic Mapping

3. Multiple Stages

Fracturing animation

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29 Sliding Sleeve with Isolation Packers

Packers are exposed to hydrocarbons and swells to create

seal with wellbore.

Completion string, consisting of sliding sleeves and packers,

is run into well.

First zone is stimulated.

Ball is dropped and second zone is stimulated.

Larger diameter ball is dropped and third zone is stimulated.

Process can be repeated for up to >30 stages

Courtesy Ken Mahrer, Apex

Horizontal Completions

Frac Baffles or Frac Sleeves

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Diversion with Expandable Packers

Sleeves are actuated with balls

Fracturing Materials

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Waterfracs

• Slickwater (water with friction reducer)

• Low sand concentrations

• 1- 5 million gallons per well

• Low fluid loss

Water Frac Fluids

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Geologic Considerations

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What is a Shale?

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“milliDarcy”

~0.1 to 10,000 mD

“microDarcy”

~0.001 to 0.1 mD

“nanoDarcy”

~0.000,010 to 0.001 mD

Now we are trying to produce

this shale that is ~1000 times

less permeable than tight sands.

And a million times less

permeable than conventional

Sands.

Courtesy, Mike Vincent, consultant

What is a Desirable Gas Shale?

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“Brittle Shale” (Complex Fracturing):

low Poisson’s Ratio & high Young’s Modulus

moderate Clay content : < 40%

bounded by frac barriers

heterogeneity

Gas-in-place (Bcf per square mile) :

30 is good, 150 is better

Permeability greater than 100 nanodarcies

Porosity: > 4%

TOC: >2% (1-3% is typical, 5-15% is great)

Moderate Water Saturation < 45%

Thick zone : >100 ft

Courtesy, Halliburton

Fracture Networks Are a Key

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What about Vertical Heterogeneity?

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Shales

Silty Shales

Mudstones

Silt Stones

Sandy laminations

What a mess!!

But they all may

produce!!!

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Determination of Fracture Barriers

Most induced fractures are vertical and are

driven toward lower horizontal stress.

For instance a fracture growing in A4

will have a difficult time breaking across

the shale above, which is higher stress

(in red), and instead will move to the

lower stress and stay in zone.

To predict where the fracture goes, you

must predict what the stresses are,

and for this, you need to know what

the rock properties are

The rock properties, such as Poisson’s

ratio and Young’s Modulus, must be

determined from cores or logs.

higher stress.

lower stress.

Horizontal Completion Technology

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Why not just a horizontal well?

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Horizontal Completions (Complex Fracturing)

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Microseismic

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Microseismic Improves Diagnostics

• Maps the fracture growth

• Identifies azimuth

• Measures frack distance

from aquifer

• Requires observation well

Microseismic

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Micro-Seismic Data Processing

3-D Velocity Grid P-wave moveout

Wellbore

Courtesy Ken Mahrer, Apex

Barnett Microseismic

Fracture Heights vs. Deepest Aquifer

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SPE 145949

Marcellus Microseismic

Fracture Heights vs. Deepest Aquifer

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SPE 145949

Shales May Have Gas, Wet Gas, or Oil

Eagleford Trend, South Texas (Source – EOG)

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Green Completions

Green completions take place during the clean-up stage of the completion, after a well has

been “fracked.”

The clean-up involves removing the water necessary to frack the well. During this flow back,

natural gas is produced with the water.

What makes the well completion “green,” or environmentally friendly, is that the gas is

separated from the water and placed in a pipeline instead of being released to the

atmosphere.

Green completions have been Devon’s standard practice in the Barnett Shale since 2004.

Devon has reduced methane emissions by more than 25 billion cubic feet in the Barnett Shale

area of north Texas during 2,000 green completions.

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Green Completions

First, a sand separator (shown at right in

this photo) filters out any sand, sending

it through a 2-inch pipe into the disposal

tank. That filtering leaves a mixture of

natural gas and water.

The second piece of equipment (in the

left side of this photo) separates the

water, which then reunites with the sand

in the disposal tank.

The gas, meanwhile, is diverted into a

separate pipe and eventually is sent by

pipeline to a processing plant.

The key to the green completion is that

a pipeline must be available for

immediate usage.

Thank you for your attention

Questions?

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